1. Field
The present invention relates generally to communications, and more specifically, to feedback decoding techniques in a wireless communications system.
2. Background
The function of a receiver in a wireless communications system is to detect a desired signal in the presence of noise, interference and other disturbances in the wireless channel. Noise arises from a variety of sources including cosmic noise, atmospheric noise, and solar noise, as well as thermal noise generated within the receiver itself. Interference, on the other hand, results from external radio transmissions. For example, in cellular communications, interference may occur between users in different cellular regions using the same carrier frequency. Interference may also occur when energy from one carrier spills over into adjacent channels. The ratio of the carrier to the interference is called the carrier-to-interference (C/I) ratio. A minimum C/I ratio is generally required to achieve a desired quality of service.
In multi-access communications systems, techniques to increase bandwidth are commonly employed to maximize user capacity. For example, many transmitter designs adaptively increase the data rate to maintain the lowest C/I ratio necessary to achieve the desired quality of service. This can be achieved by estimating the C/I ratio, or other quality parameter, at the receiver and providing feedback to the transmitter to control the data rate. The effectiveness of this approach depends on the ability of the transmitter to decode the feedback. Increasing the power of the feedback is not always a viable approach because it tends to increase the interference for other users. Accordingly, efficient decoding techniques are needed to increase the reliability of the feedback at the transmitter.